In drilling an oil well, it is first necessary to situate a blowout preventer and drilling rig structure before drilling can begin. Blowout preventers and drilling rigs vary in size and configuration. The framework which supports a drilling rig is varied in configuration so that access to the underside, while always available, is different from job to job. This difference is sometimes accentuated by customer requirements as, for example, specified casing connections which modify the elevation of the blowout preventer relative to the drilling rig. The blowout preventer may stand tall in one installation; the same equipment used for another customer will be configured differently as a result of terrain and customer requirements. Variations in terrain and working area also modify the location of the mud tanks. They may be arranged at any relative angular direction from the drilled hole. As will be understood, the mud flows through the drill string and returns up the annulus to be returned to the mud pits. It is necessary to construct a mud return line from the cased hole to the pits.
In the past, the problem of erecting the drilling rig and all the associated equipment has been handled on an ad hoc basis. This has required the services of welders and pipe fitters at the site. They typically position the major structural members such as the drilling rig with its supporting framework therebeneath and also position the blowout preventer in the manner and position specified by the customer. Thereafter, through the use of support chains, spare frame members, surplus pipe and the like, a funnel is typically welded in position to handle the annular upflow of drilling mud. The funnel is typically cut, and a nipple is attached. The nipple is then connected by welding or custom fittings to some kind of lateral mud line which drains into the mud tanks. The mud flow line typically must weave and snake its way through the framework beneath the drilling rig.
The mode of construction described above is tedious and typically delays installation of the drilling rig preparatory to drilling operations. The delays are costly, not only in labor of the welding personnel, but they are costly in that rig rental time is expensive.